Problem: Solve for $z$ : $23 + z = 25$
Answer: Subtract $23$ from both sides: $ \begin{eqnarray} \\ 23 + z &=& 25 \\ \\ {-23} && {-23} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{23 + z} &\hphantom{=}& \hphantom{25} \\ z &=& 25 {- 23} \\ \end{eqnarray} $ Simplify. $ z = 2$